The pre-sear (which can be lighter than the post-sear) adds flavor, but also makes the (important) post-sear much faster, which also minimizes the degree to which the post-sear will raise the interior temperature of your protein.
The pre-sear is especially important with long cooks, because it kills surface bacteria. The first time you get too much lactobacillus hitching a ride on your short ribs will be the last time you skip out on the pre-sear. (Lacto isn't dangerous; after all, the protein is pasteurized in the bath, but the final product will smell awful).
I'm not sure what you mean by "drying out the edges, making them leathery". I think I can just say "no" on that.